The external cover of aeroplane is made up of aluminium instead of iron. why?

In positive numbers less than 1, the zeros between the decimal point and a non-zero number are blank significant

Along the line connecting the two charges, at what distance from the charge q1 is the total electric field from the two charges zero? express your answer in terms of some or all of the variables s, q1, q2 and k =14ï€ïµ0. if your answer is difficult to enter, consider simplifying it, as it can be made relatively simple with some work.

When using the scientist method, which step comes last?